Statistical techniques for the classification of chromites in diamond exploration samples     

W.L. Griffin  N.I. Fisher  J.H. Friedman  C.G. Ryan 《Journal of Geochemical Exploration》1997,59(3):233-249

A database of 1267 quality-screened major- and trace-element analyses of chromites (s.l.) from kimberlites, lamproites, ultramafic lamprophyres (UMLs) and crustal sources (‘greenstones’, including ophiolites, gabbros, basalts and komatiites) has been subjected to statistical analysis, in order to derive discriminants for use in diamond exploration. The techniques used included nearest-neighbour analysis, CART (classification and regression trees) and MARS (multivariate adaptive regression splines). The results show that both CART and MARS approaches can correctly discriminate kimberlite/lamproite chromites from UML/‘greenstone’ chromites at levels near 90%. Discrimination into the four classes separately is achieved at levels of ca. 80% by MARS and > 70% by CART; much of the misclassification is between the kimberlite and lamproite classes. These results probably represent the maximum probable level of discrimination on chemical criteria, given that ascending magmas may sample both mantle and crustal rocks. The CART approach produces a classification tree that requires no further computation to classify a given grain; the MARS approach requires the use of a simple software package. Tests on known samples illustrate the high level of accuracy of the methods in an exploration context, as well as the useful petrogenetic conclusions that can be drawn from some ‘misclassifications’.  相似文献   

Fluvial process and the establishment of bottomland trees   总被引：1，自引：0，他引：1  

Michael L. Scott  Jonathan M. Friedman  Gregor T. Auble 《Geomorphology》1996,14(4):327-339

The effects of river regulation on bottomland tree communities in western North America have generated substantial concern because of the important habitat and aesthetic values of these communities. Consideration of such effects in water management decisions has been hampered by the apparent variability of responses of bottomland tree communities to flow alteration. When the relation between streamflow and tree establishment is placed in a geomorphic context, however, much of that variability is explained, and prediction of changes in the tree community is improved.The relation between streamflow and establishment of bottomland trees is conditioned by the dominant fluvial process or processes acting along a stream. For successful establishment, cottonwoods, poplars, and willows require bare, moist surfaces protected from disturbance. Channel narrowing, channel meandering, and flood deposition promote different spatial and temporal patterns of establishment. During channel narrowing, the site requirements are met on portions of the bed abandoned by the stream, and establishment is associated with a period of low flow lasting one to several years. During channel meandering, the requirements are met on point bars following moderate or higher peak flows. Following flood deposition, the requirements are met on flood deposits ;high above the channel bed. Flood deposition can occur along most streams, but where a channel is constrained by a narrow valley, this process may be the only mechanism that can produce a bare, moist surface high enough to be safe from future disturbance. Because of differences in local bedrock, tributary influence, or geologic history, two nearby reaches of the same stream may be dominated by different fluvial processes and have different spatial and temporal patterns of trees. We illustrate this phenomenon with examples from forests of plains cottonwood (Populus deltoides ssp. monilifera) along meandering and constrained reaches of the Missouri River in Montana.  相似文献   

Processes controlling precipitation of carbonate cement and dissolution of silica in reef and near-reef settings     

Samuel A. Epstein  Gerald M. Friedman 《Sedimentary Geology》1982,33(3):157-171

Carbonate cementation in the surface layer of reefs and beachrock eliminates porosity and partially replaces detrital quartz grains. The uptake and release of CO₂ by photosynthesis and respiration in reef communities cause a shift in the carbonate buffer system of seawater. Field studies and experimentation simulating the natural settings show minimum values of CO₂ (1.9 mmoles 1^?1) and HCO₃^? (2.4 meq 1^?1) in association with maximum values of pH (9.8) and O₂ (> 100% oxygen saturation) in waters covering corals and algae prior to sunset. The converse is true for these variables prior to sunrise, when minimum values of pH (7.6) and O₂ (<66% oxygen saturation) occur with maximum values of CO₂ (2.7 mmoles 1^?1) and HCO₃^? (2.7 meq 1^?1). Experimental tanks containing plain seawater showed almost no diurnal variability in pH (a constant 7.5–7.6) or O₂ (80–90% oxygen saturation) measurements. Seawater adjacent to reef biomass, with elevated pH and supersaturated with calcium carbonate, is periodically pumped into the underlying reef and beach sediments due to pressure-buildups between the reef framework or algal zones and open waters. Carbonate precipitation and quartz dissolution follow. As the system equilibrates, pH values progressively decrease.  相似文献   

Textures of sandstones and carbonate rocks in the world's deepest wells (in excess of 30,000 ft or 9.1 km): Anadarko Basin,Oklahoma—Reply     

Gerald M. Friedman 《Sedimentary Geology》1983,35(2):156-157

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Isotopic composition of oil-field brines from Kettleman North Dome,California, and their geologic implications     

Yousif K Kharaka  Frederick A.F Berry  Irving Friedman 《Geochimica et cosmochimica acta》1973,37(8):1899-1908

Deuterium and O¹⁸ analyses were made on 25 formation-water samples from Miocene (Temblor Formation) and Eocene (McAdams Formation) reservoir rocks at Kettleman North Dome oil field, California, and on three surface water samples from Reef Ridge located about three miles to the west of the field. The δO¹⁸ values obtained generally increase with depth and most probably are due to temperature controlled exchange reactions with carbonate cement and dissolved carbonate species. The δD values obtained seem to be controlled primarily by the membrane behavior of shales modifying the assumed original values. The contribution of isotopic exchange between water and clays cannot be evaluated at present.The isotopic data support the conclusions based on a detailed study of geology, hydrodynamics, and formation water geochemistry (Kharaka, 1971) which indicate that:1. The Temblor Formation waters are probably meteoric in origin concentrated chemically and isotopically by shale membranes, and 2. The McAdams Formation waters were most probably obtained by squeezing the original interstitial marine connate waters of deposition from the underlying Mesozoic sediments.  相似文献   

Obsidian hydration dating of volcanic events     

Irving Friedman  John Obradovich 《Quaternary Research》1981,16(1):37-47

Obsidian hydration dating of volcanic events had been compared with ages of the same events determined by the ¹⁴C and KAr methods at several localities. The localities, ranging in age from 1200 to over 1 million yr, include Newberry Craters, Oregon; Coso Hot Springs, California; Salton Sea, California; Yellowstone National Park, Wyoming; and Mineral Range, Utah. In most cases the agreement is quite good. A number of factors including volcanic glass composition and exposuretemperature history must be known in order to relate hydration thickness to age. The effect of composition can be determined from chemical analysis or the refractive index of the glass. Exposure-temperature history requires a number of considerations enumerated in this paper.  相似文献   

Light element geochemistry of the Apollo 12 site     

J.F. Kerridge  I.R. Kaplan  C.C. Kung  D.A. Winter  D.L. Friedman  D.J. DesMarais 《Geochimica et cosmochimica acta》1978,42(4):391-402

Analytical techniques of improved sensitivity have revealed details of the concentrations and isotopic compositions of light elements for a comprehensive suite of samples from the Apollo 12 regolith. These samples show a wide spread in maturity, although maximum contents observed for solar wind elements are less than observed at other sites, possibly reflecting relative recency of craters at the Apollo 12 site. Isotopic composition of nitrogen is consistent with the idea that ¹⁵N/¹⁴N in the solar wind has increased with time, at least a major part of this increase having occurred in the past 3.1 Gyr. Sulfur isotope systematics support a model in which sulfur is both added to the regolith, by meteoritic influx and lost, by an isotopically selective process. Most soils from this site are heavily contaminated with terrestrial carbon.  相似文献   

Evaluation of cold-water carbonates as a possible paleoclimatic indicator     

Jay E. Leonard  Barry Cameron  Orrin H. Pilkey  Gerald M. Friedman 《Sedimentary Geology》1981,28(1):1-28

The common belief currently shared by many geoscientists concerning the climatic interpretation of limestones is that a warm-water environment is essential. This concept is not necessarily true because the rate and extent of terrigenous sediment dilution, rather than water temperature, is the primary factor determining whether or not a limestone forms at nearshore or continental shelf depths. Because carbonate productivity is lowest in cold climates, however, CaCO₃ abundance and the thickness of carbonate accumulations tend to be least at high latitudes. In this regard present-day continental shelves and beaches offer a poor model for comparing cold-water and warm-water carbonates because of the generally emergent continental tectonic framework, recent eustatic sea-level changes, and the presence of ice caps at the modern poles.Typically, the influence of climate on non-reef continental shelf and beach environments cannot be clearly distinguished by the presence or absence of major taxonomic groups. Faunal diversity and equitability are more sensitive in this regard. The absence of shelf-depth inorganic carbonate precipitates, micrite envelopes, and peloids may also point to the cold-water origin of a rock. Skeletal mineralogy and oxygen isotopes of certain unrecrystallized carbonates may be good paleoclimatic indicators; however, trace elements and physical-textural attributes of the carbonate fraction are probably temperature insensitive.Previous studies of high-latitude continental shelves have concentrated merely on the abundance of calcareous material and there is seemingly a disproportionate amount of information with respect to low-latitude carbonate studies. Further research on cold-water carbonates may open up new avenues for alternative paleoenvironmental and paleoclimatic interpretations.  相似文献   

Metasomatized lithospheric mantle beneath Turkana depression in southern Ethiopia (the East Africa Rift): geochemical and Sr–Nd–Pb isotopic characteristics     

Daniel Meshesha  Ryuichi Shinjo  Risa Matsumura  Takele Chekol 《Contributions to Mineralogy and Petrology》2011,162(5):889-907

Mantle xenoliths entrained in Quaternary alkaline basalts from the Turkana Depression in southern Ethiopia (the East Africa Rift) were studied for their geochemical and Sr–Nd–Pb isotopic compositions to constrain the evolution of the lithosphere. The investigated mantle xenoliths are spinel lherzolites in composition with a protogranular texture. They can be classified into two types: anhydrous and hydrous spinel lherzolites; the latter group characterized by the occurrences of pargasite and phlogopite. The compositions of whole-rock basaltic component (CaO = 3.8–5.6 wt%, Al₂O₃ = 2.5–4.1 wt%, and MgO = 34.7–38.1 wt%), spinel (Cr# = 0.062–0.117, Al₂O₃ = 59.0–64.4 wt%) and clinopyroxene (Mg# = 88.4–91.7, Al₂O₃ = 5.2–6.7 wt%) indicate that the lherzolites are fertile and have not experienced significant partial melting. Both types are characterized by depleted ⁸⁷Sr/⁸⁶Sr (0.70180–0.70295) and high ¹⁴³Nd/¹⁴⁴Nd (0.51299–0.51348) with wide ranges of ²⁰⁶Pb/²⁰⁴Pb (17.86–19.68) isotopic compositions. The variations of geochemical and isotopic compositions can be explained by silicate metasomatism induced by different degree of magma infiltrations from ascending mantle plume. The thermobarometric estimations suggest that the spinel lherzolites were derived from depths of 50–70 km (15.6–22.2 kb) and entrained in the alkaline magma at 847–1,052°C. Most of the spinel lherzolites from this study record an elevated geotherm (60–90 mW/m²) that is related to the presence of rising mantle plume in an active tectonic setting. Sm–Nd isotopic systematic gives a mean T_DM model age of 0.95 Ga, interpreted as the minimum depletion age of the subcontinental lithosphere beneath the region.  相似文献   

Book reviews     

George Kish  Wolf Tietze  C. Paddick  Dietrich Barsch  Keith Clayton  Michael F. Thomas  Thomas Peucker  Alexander Zaporozec  Georg Matthess  German Müller  K. Ernstson  Olusegun Areola  Gerald M. Friedman  Maurice K. -Seguin  C. Koeman  Risto Aario 《GeoJournal》1979,3(4):410-416

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